The aim of this project is to develop animal models appropriate for studing the physiological mechanisms associated with the condition of stable weight maintenance at different levels. To study weight maintenance at elevated or obese levels, we propose to use 1) the genetically obese Zucker rat, 2) the ventromedial hypothalamic lesioned rat, and 3) the dietary obese rat. As a model of weight maintenance at reduced levels we will use the lateral hypothalamic lesioned rat. By studying these preparations, we hope 1) to gain a better understanding of how energy balance is achieved at widely different levels, 2) to establish criteria by which we can judge whether or not the maintained energy levels in different preparations result from abnormally high or low "set-points" or from regulatory failure, 3) to examine the adjustments in whole body metabolism that serve to maintain the regulated or "set-point" level of body energy, 4) to explore the role of the autonomic nervous system in setting the weight levels at which normal energy balance is reached, 5) to use parasympathetic and sympathetic manipulations to establish lower or higher regulation levels, and 6) to normalize "set-points" using such autonomic manipulations in rats which regulate body weight at elevated or reduced levels. An understanding of these processes and the identification of their features should have direct application to the diagnosis and treatment of weight disorders in humans.